Valve apparatus

ABSTRACT

The invention relates to a valve apparatus for setting and monitoring the clamping pressure of a clamping device ( 9 ) for workpieces which are to be clamped, in particular in lathes, having at least one pressure control valve ( 1 A,  1 B), via which the clamping pressure is set for the clamping device ( 9 ), and having at least one pressure sensor ( 6 A,  6 B) which detects the respective clamping pressure of the clamping device ( 9 ), which clamping pressure is to he adjusted in relation to a predefinable setpoint clamping pressure. It is possible by way of the valve apparatus to this effect to set the clamping pressure which is relevant in terms of safety, and also to monitor it, in particular to maintain or reduce it, during the machining in the sense of an adjustment.

The invention relates to a valve apparatus for setting and monitoringthe clamping pressure of a clamping device for workpieces which are tobe clamped, particularly in lathes.

In modern machine tools, for example lathes, the workpieces to bemachined are generally clamped by means of clamping devices which can behydraulically actuated, particularly in the form of clamping cylinders,and/or are secured tightly by means of so-called tailstock spindlesleeves which can be hydraulically actuated, with the respective machinebeing released only after the clamping pressure is reached. If, at thispoint during machining with the machine tool, the clamping pressure onthe clamping device is reduced due to a fault, this can lead toloosening of the clamping device, and the subsequently releasedworkpiece can cause serious damage to the machine and constitutes aconsiderable safety risk for the machine operator.

In addition to this monitoring of the clamping pressure to ensure safeclamping forces, it can also be advantageous to reduce the clampingpressure, and therefore the clamping force, in order to prevent damageto the machined workpiece if it acquires a wall thickness geometry thathas been reduced from “full bored,” for example, as a result of the typeof machining and which, with the clamping force remaining the samerelative first of all to the solid material used, would lead to thedeformation of workpiece geometries that are reduced in wall thicknessand therefore are weakened.

Proceeding from this prior art, the object of the invention is toincrease safety in the clamping accommodation of workpieces to bemachined in machine tools such as lathes, and to prevent inadvertentdamage to the workpiece. This object is achieved by the valve apparatuswith the features of claim 1 in its entirety.

The valve apparatus according to the invention is characterized in thatit has at least one pressure control valve via which a clamping pressureadjustment for the clamping device takes place, there being at least onepressure sensor that detects the respective clamping pressure of theclamping device which is to be adjusted to a definable setpoint clampingpressure. With this valve apparatus, it is possible to set the clampingpressure which is relevant to safety engineering and also to monitor itduring machining for purposes of adjustment, in particular to maintainor reduce it uniformly.

Using the respective pressure sensor, the current pressure of theclamping device is measured, whether in the form of the clampingcylinder which is to be hydraulically actuated or in the form of atailstock spindle sleeve which is to be hydraulically actuated. Thiscurrent clamping pressure should then correspond to a predefinedsetpoint clamping pressure which can be predefined by the control means,for example, in the form of a machine control for the machine tool. Bytriggering the pressure control valve, preferably in the form of apressure reducing valve, the pressure of the clamping device can be setto constant pressure values or even reduced by means of triggering bymeans of the control means. Since, essentially for each workpiece to bemachined according to the desired machining state, there are otherclamping pressure constraints, they are defined in near real time as asetpoint clamping pressure by the control of the machine, that is tosay, by the control means, as machining progresses. This ensuresreliable clamping force monitoring in order to prevent the workpiecefrom unintentionally coming loose from the clamping device. Furthermore,it becomes possible, if necessary, to reduce the clamping force in orderto protect the workpiece during machining against damage from aclamping-compressive force that has been set too high.

Other advantageous configurations of the valve apparatus according tothe invention are the subject matter of the other dependent claims.

The valve apparatus according to the invention is detailed below usingdifferent exemplary embodiments as shown in the drawings. The figuresare schematic in the manner of hydraulic diagrams.

FIG. 1 shows a first embodiment of the valve apparatus according to theinvention using a pressure control valve;

FIG. 2 shows another embodiment as shown in FIG. 1 using two pressurecontrol valves; and

FIG. 3 shows a third embodiment of the valve apparatus according to theinvention as shown in FIGS. 1 and 2, but with a secondary pressuresafeguard and with the elimination of the directional control valves.

In the three embodiments, fundamentally comparable components, inparticular valve components, are used and designated with the samereference numbers. The main components are as follows:

-   1A, 1B pressure control valves with mechanical self-locking,-   2 orifice,-   4A, 4B directional control valves with latching (self-retaining)    positions,-   5 back pressure block in the form of a check valve,-   6A, 6B pressure sensors,-   7 rotary duct,-   8 two check valves,-   9 clamping cylinder made as a synchronous cylinder-   10 clamping chuck with small transmission ratio (without    self-locking)-   11 hydraulic accumulator-   12 control

The clamping cylinder, designated as 9 in the figures, is made as aso-called hydraulic synchronous cylinder, and the jaws of the clampingchuck 10 in one direction of motion are moved toward one another and inthe opposite direction are moved away from one another. In this way, aworkpiece to be machined (not shown) can be detachably fixed with ahydraulic actuation force both by way of the inside diameter and also inthe other actuation direction by way of the outside diameter of theclamping jaws of the clamping chuck.

The rotary duct designated as 7 allows pivoting of the clamping devicein at least one axis of motion or pivoting. These rotary ducts forhydraulic feed and drain lines are known in the prior art in a pluralityof embodiments so that they will not be detailed any further here. Inany case, in this way it is ensured by way of the rotary duct 7 thathydraulic supply of the working spaces of the clamping cylinder 9 takesplace even when the clamping cylinder 9 is being pivoted with theclamping chuck 10. The clamping device which consists of the clampingcylinder 9 and the clamping chuck 10 is shown merely by way of example;different types of clamping devices (tailstock spindle sleeves) canlikewise be used here for the valve apparatus which is still to bedescribed.

The orifice designated as 2 on the output side of the respectivepressure control valve 1A, 1B is used to adapt the volumetric flow tothe volumetric size of the clamping cylinder 9, which, depending on thetype of machining, can also be different for a machine tool. The fluidline designated as P is connected to a hydraulic supply means (notdetailed), for example is formed from a hydraulic supply pump. Thehydraulic accumulator, which is designated as 11 and which is connectedto the pump line P, then allows pressure supply of the system when thepower fails. The tank connecting line or tank line designated as Tallows return of the working medium in the form of hydraulic oil intothe tank, from where hydraulic supply can take place via the pump withthe formation of a hydraulic circuit. This arrangement is alsoconventional so that it will not be detailed any further here.

In the embodiment as shown in FIG. 1, the clamping pressure for theclamping cylinder 9 can be set by way of the pressure control valve 1Awith mechanical self-locking, and the value can be displayed on thedigital display of a conventional electronic control 12, which displayis not detailed. To set the predefinable clamping pressure value, thiscontrol 12, which is shown in FIG. 1 as a black box, therefore triggersthe motor M of the pressure control valve 1A which moreover is connectedto the pressure sensors 6A, 6B, in order in this way to detect theactual pressure prevailing in the utility connections A, B, which are,in turn, each connected to the pertinent working spaces of the clampingcylinder 9 to carry fluid via the check valves 8. By means of thecontrol 12, the operator can therefore freely stipulate thecorresponding pressure values for the pressure control valve 1A, ortriggering takes place by way of a corresponding program for control 12;for different workpieces to be clamped, different programming isprovided which, in turn, is freely selectable within a definableframework. The predefined pressure, set by hand or by way of therespective machine control program, is therefore accepted in thisrespect and is continuously monitored within the framework of furthermachining. If the clamping pressure on the clamping cylinder 9 thendrops, for example, as a result of technical failure, this can bedetected by way of the respectively assignable pressure sensor 6A, 6B,and a corresponding error message then travels to the control 12, withthe result that it shuts off the assignable machine drive on themetal-cutting machine for the clamping device; this takes place in nearreal time. In this way, damage to the metal-cutting machine and/or theworkpiece to be machined is avoided. Depending on the programming, theclamping pressure can be monitored both for internal clamping and alsofor external clamping by means of the clamping chuck 10 of the clampingcylinder 9.

While setting of the clamping pressure takes place on the valve 1A, theactual clamping takes place by actuating the valve 4A, while the valve4B is not actuated. The valves 4A, 4B used are made in the form ofdirectional control valves with locking (self-locking) positions, andthey can be shifted into the respective actuating positions by way ofassignable electrical control magnets S1, S2, S3, and S4 in order inthis way to be able to move the clamping cylinder 9. If the valve 4A hasbeen actuated, the clamping pressure is monitored by the pressure sensor6A, conversely, at the same time there should not be any back pressureon the pressure sensor 6B; otherwise, this would be an indication of amalfunction. If the clamping cylinder 9 is to be relieved, in order, forexample, to release the workpiece to be machined, then switching ofvalve 4B takes place while valve 4A is switched back into its initialposition. As FIG. 1 shows, one output of the respective directionalcontrol valve 4A, 4B is blocked fluid-tight by way of a correspondingsealing plug since in this respect this output is not necessary for thevalve function intended here.

According to the operating description as shown in FIG. 1, the two checkvalves 8 are interconnected such that they are connected to be able tobe mutually unblocked and are connected on their blocking inlet sideboth to the assignable utility connection A and also to the utility‘connection B. The back pressure block 5, which is made as a checkvalve, prevents a dynamic pressure which may build up in the tank line Tfrom unintentionally changing the clamping force on the clampingcylinder 9. The valve components used for the valve apparatus accordingto the invention are standard components and can be economically madeavailable and are moreover reliable in use. Furthermore, the pressurecontrol valve 1A on the one hand is connected to the fluid line P withthe hydraulic accumulator 11 and is connected to the directional controlvalves 4A and 4B respectively to carry fluid by way of the orifice 2.

With the valve apparatus which has been described in this way as shownin the circuit of FIG. 1, when the clamping pressure drops, the machinecan be shut down in order thus to meet increased safety requirements.Moreover, the solution as shown in FIG. 1 allows a reduction of theclamping force in order to help avoid deformations of the workpiecewhich can arise, for example, as a result of the fact that duringmachining first a solid profile workpiece is clamped, which then becomesa hollow profile in metal cutting, with reduced wall thickness whichcould otherwise be deformed when the clamping force remains the same.

For this purpose, the exemplary embodiment as shown in FIG. 1, in turn,calls for setting the clamping pressure on the valve 1A which ispreferably made as a proportional pressure reducing valve. A clampingprocess by way of the clamping cylinder 9 takes place by actuating thevalve 4A, while the valve 4B remains in its position shown in FIG. 2. Inthe utility connection A then the clamping pressure is monitored on thepressure sensor 6A, while at the same time there should be little or noback pressure on the pressure sensor 6B. Relief then takes place byswitching the valve 4B, while the valve 4A is, in turn, switched backinto the initial position as shown in FIG. 1. Within the scope of thisspecification, it is fundamentally assumed that, by applying pressure inthe utility line A with simultaneous discharge of hydraulic oil from theutility line B, a clamping process is initiated via the clampingcylinder 9 and the clamping chuck 10; by reversing this function, arelief process is carried out. When there is a change from insideclamping to outside clamping relative to the clamping jaws of theclamping chuck 10, the aforementioned statements then, however, apply inreverse.

For reducing the clamping pressure with only one pressure regulator 1Aas shown in FIG. 1, as already described, the clamping pressure is seton the valve 1A by means of the control 12, and relief takes place byswitching of valve 4A. At the same time, monitoring of the clampingpressure takes place by means of the pressure sensors 6A, 6B which relaytheir values to the control 12 of conventional design. If at this pointthe valve 4B is switched, the clamping pressure in the utility lines A,B is equalized, the check valves 8 are both opened, and pressureequalization takes place in the clamping cylinder 9. Since self-lockingdoes not occur in the clamping chuck, the clamping force is lowered tozero.

The level of the clamping pressure on the pressure regulator 1A can nowbe lowered to the desired level, and the clamping pressure drops inlines A and B and, as a result of the opened check valve 8, also dropsin the clamping cylinder 9. The clamping force then remains at zero.After completed switching back of the valve 4B, the pressure in theutility line B and on the relief side of the clamping cylinder 9 isreduced, and the clamping force is built up again at a lower level onthe clamping chuck 10 by the prevailing pressure in the utility line A.In this way, the indicated minimization of the clamping force isachieved.

The solution as shown in FIG. 1 therefore uses two 4/2 directionalcontrol valves 4A, 4B, of which, viewed in the direction of looking atFIG. 2, the output on the left leads into a blind connection.Furthermore, the valves 4A, 4B are connected to the respectivelyassignable back pressure block 5 which is connected to the tank line Trespectively. The outputs of the pressure sensors 6A, 6B are connectedto the machine control 12 shown as a black box for reducing the clampingpressure force for evaluation of the respective measurement signal, thecontrol 12 for stipulation of a pressure setpoint having a manual inputwhich is not detailed or has a freely programmable flow diagram(program).

If it should not be possible to ensure that, when the clamping pressureis equalized, the friction is sufficient for actually holding theworkpiece in the clamping chuck 10, the embodiment as shown in FIG. 2with two pressure regulators 1A, 1B would be appropriate. This reductionof the clamping pressure then calls for a pressure just below the levelin the utility line A to be set on the pressure control valve 1B. Withthe switching of valve 4B, a back pressure is then built up in theutility line B, and the check valves 8 are both opened. Sinceself-locking does not occur in the clamping chuck 10, the clamping forceis reduced to a low value. As a result, the pressure on the valves 1Aand 1B is lowered until the desired level is reached in the utility lineA. The pressure difference between the valves 1A and 1B must bemaintained in this process. Owing to the opened check valves 8, theclamping pressure also drops in the clamping cylinder 9 with the resultthat the clamping force remains at a constant low level.

By switching back the valve 4B, the pressure in the utility line B andon the relief side of the clamping cylinder 9 is reduced. The clampingforce is then built up again at a lower level on the clamping chuck 10by the pressure in the utility line A.

Instead of using 4/2 directional control valves, the embodiment as shownin FIG. 2 is equipped with motorized 3/2 directional control valves 4A,4B. Furthermore, the 2-way pressure regulators shown in FIGS. 1 and 2can also be replaced by 3-way pressure regulators.

The embodiment as shown in FIG. 3 differs from the two precedingembodiments in that neither directional control valves with latchingpositions as shown in FIG. 1 nor motorized 3/2 directional controlvalves according to the embodiment as shown in FIG. 2 are required.Rather in the solution as shown in FIG. 3, only two proportionalpressure reducing valves 1A, 1B are used which acquire a secondarypressure safeguard via the respective back-pressure blocks 5. For thesake of simplicity, in FIGS. 2 and 3 in the embodiments there, thecontrol 12 with its corresponding connection sites was not shown, but inthis respect the embodiments relating to the solution as shown in FIG. 1apply.

The valve apparatus according to the invention is advantageous in thatin a modular construction it can also be retrofitted onto existingworkpiece chucking fixtures in machine tools. As a result of the modularblock structure of the valve apparatus, it takes up less installationspace and is economical to implement because of the standard componentswhich can be used.

1. A valve apparatus for setting and monitoring the clamping pressure ofa clamping device (9) for workpieces which are to be clamped,particularly in lathes, with at least one pressure control valve (1A,1B) via which a clamping pressure adjustment for the clamping device (9)takes place, and with at least one pressure sensor (6A, 6B) whichdetects the respective clamping pressure of the clamping device (9)which is to be adjusted to a definable setpoint clamping pressure. 2.The valve apparatus according to claim 1, characterized in that therespective pressure control valve is a pressure reducing valve (1), inparticular a proportional pressure reduction valve (1A, 1B).
 3. Thevalve apparatus according to claim 1, characterized in that therespective pressure control valve (1A, 1B) is provided with mechanicalself-locking which is preferably formed by self-locking gearing of apositioning motor (M) which can be triggered by the control means. 4.The valve apparatus according to claim 1, characterized in that therespective pressure sensor (6A, 6B) is connected to an electroniccontrol (12) or that the pressure sensor is part of an electronicpressure switch which can be freely programmed.
 5. The valve apparatusaccording to claim 1, characterized in that at least two 3/2 directionalcontrol valves (4A, 4B) or two 4/2 directional control valves (4A, 4B)are used to supply the clamping device (9).
 6. The valve apparatusaccording to claim 1, characterized in that two directional control (4A,4B) valves and/or pressure control valves (1A, 1B) can be switchedindependently of one another.
 7. The valve apparatus according to claim5, characterized in that the respective directional control valve (4A,4B) is connected to a hydraulic supply circuit between the assignablepressure control valve (1A, 1B) and the clamping device (9).
 8. Thevalve apparatus according to claim 1, characterized in that the clampingdevice (9) has two check valves (8) which are connected to one anotherto carry fluid and which assume their blocking position in the directionof the respective pressure reducing valve (1A, 1B).
 9. The valveapparatus according to claim 8, characterized in that the two checkvalves (8) are connected to the respective output of the assignabledirectional control valve (4A, 4B) to carry fluid.
 10. The valveapparatus according to claim 1, characterized in that, to adapt to thevolumetric size of the clamping device (9) used at the time, an orifice(2) is used which is located on the output side of the respectivepressure reducing valve (1A, 1B).
 11. The valve apparatus according toclaim 1, characterized in that, with the omission of directional controlvalves, it has two pressure control valves (1A, 1B).